There are numerous instances in which it is desirable to measure the load on a rigid structural member. In such load measurements, the principal load components of interest are the forces along orthogonal x, y and z axes and the moments about those orthogonal axes. Some of the applications for load measurement apparatus are: machine tools, in which it is desirable to measure the load on a cutting or boring tool by measurement of the components of load on a tool holder supporting the tool or on a spindle or tool post supporting the tool holder; engine test stands, in which it is desirable to measure the thrust produced by a rocket or turbine engine by measurement of the components of load on the portions of the test stand supporting the engine; and, robotics, in which it is desirable to measure the components of load on the grippers, end effectors, wrists and arms of an industrial robot.
Notwithstanding the application, it is essential that the load measurement apparatus provide accurate and precise static and dynamic load measurements, that the load measurement apparatus be inexpensive, rugged, thermally stable, and easy to calibrate, that the components of the load measurement apparatus be easy to install and replace, and that the load measurement apparatus not add significant compliance to the structural member or to the supporting structure therefor. It is to the end of achieving each of these objectives that the present invention is directed.